In some cases, it is necessary to detect a resonant frequency in a resonant space. For example, when acoustic equipment such as a speaker is installed in a hall or a gymnasium to radiate a loud sound wave from a speaker, music or voice from the speaker is sometimes difficult to listen to because of the presence of a resonant frequency in this space (loud sound space in which the acoustic equipment is installed). To be specific, if the loud sound wave from the speaker contains a component of the resonant frequency in large amount, resonance occurs in a frequency of this component in the loud sound space. A resonant sound is like “won . . . ” or “fan . . . .” The resonant sound is not a sound wave to be radiated from the speaker and makes it difficult to listen to the music or the voice from the speaker.
To avoid this, the resonant frequency in the loud sound space is detected, and a dip filter or the like is provided at a forward stage of the speaker in the acoustic equipment to attenuate the component of the resonant frequency. Thereby, resonance is unlikely to occur in this loud sound space, making it easy to listen to the music or the voice from the speaker. In order to determine a frequency characteristic of the dip filter, it is necessary to first detect the resonant frequency in the loud sound space.
Traditionally, an operator or a measuring person for the acoustic equipment has distinguished the loud sound from the speaker or the resonant sound depending on their senses of hearing to make judgment of the resonant frequency.
However, some skill or experience is required to distinguish the sound for judgment of the resonant frequency depending on the senses of hearing. Such detection of the resonant frequency depending on the skill or experience is not always accurate. Further, this has impeded automatic measurement and automatic adjustment of the acoustic equipment installed in the loud sound space or the like.